collect + Iterators.Stateful + Base.Generator lose last element

[jacg]

julia> collect(Iterators.Stateful(2x for x in 1:3))
2-element Vector{Int64}:
 2
 4

The input has 3 elements, I would therefore expect the output also to have 3 elements, but there are only 2.

On the other hand, the problem disappears if

• we remove the generator

  collect(Iterators.Stateful(1:3))
  3-element Vector{Int64}:
   1
   2
   3
  

• we use iterate directly

  julia> s = Iterators.Stateful(2x for x in 1:3);
  
  julia> iterate(s)
  (2, nothing)
  
  julia> iterate(s, ans[2])
  (4, nothing)
  
  julia> iterate(s, ans[2])
  (6, nothing)
  
  julia> iterate(s, ans[2])
  
  julia> 
  

versioninfo

julia> versioninfo()
Julia Version 1.6.1
Commit 6aaedecc44 (2021-04-23 05:59 UTC)
Platform Info:
  OS: Linux (x86_64-pc-linux-gnu)
  CPU: Intel(R) Core(TM) i7-3632QM CPU @ 2.20GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-11.0.1 (ORCJIT, ivybridge)

julia> 

The problem also appears in julia 1.3.1, but it seems to be behaving as expected in 1.0.

Edit:

My 1.3.1 trial was in an online REPL (https://replit.com/languages/julia) which claims to be 1.3.1 but versioninfo() shows 1.4.1

julia version 1.3.1
 versioninfo()
Julia Version 1.4.1
Commit 381693d3df* (2020-04-14 17:20 UTC)
Platform Info:
  OS: Linux (x86_64-pc-linux-gnu)
  CPU: Intel(R) Xeon(R) CPU @ 2.30GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-8.0.1 (ORCJIT, haswell)

 collect(Iterators.Stateful(2x for x in 1:3))
2-element Array{Int64,1}:
 2
 4

[simeonschaub]

Duplicate of #35530, should be fixed now by #41919.